This invention relates to enhancing the communication capabilities of a core satellite communication system, and more particularly relates to such a system in which supplemental communications can be performed aboard a supplemental satellite launched after the core satellite.
The long operational lifetimes of orbiting communication satellites or spacecraft present a dilemma for designers of the communication systems included in such spacecraft. Large, high capacity spacecraft with provisions for currently-required ground to satellite network connectivity are expensive, and their associated launch costs are substantial. As a result, there is a tendency to procure the largest, longest lifetime spacecraft possible.
However, deploying spacecraft with the longest lifetime possible presents problems in the context of the present communications industry which is changing rapidly and which is expected to serve new markets, possibly requiring direct connectivity between satellites, in the future. However, the details of the new markets and services are not clear and have not been defined. With spacecraft communications in such a state of flux, some consultants have publicly advised against deploying spacecraft with operational lifetimes longer than about five years.
The current preference in commercial spacecraft is for stand-alone spacecraft with interconnection through ground terminals that have simultaneous visibility to multiple satellites (i.e., multi-hop, ground bounce). It is widely accepted that high capacity inter-satellite links will eventually become cost effective in satellite communications networks, but current economics weigh against their deployment at this time. There is a need for an approach that allows deployment of large, expensive spacecraft optimized for current network operations whose connectivity can be expanded at a future time to include long range intersatellite links.
Communication satellites are generally deployed in a defined orbital slot which consists of a geographical location and a band of frequencies which are authorized for receipt and transmission of communication signals. The acquisition of an orbital slot requires substantial effort and expense. There is a need for communication circuit techniques which enable the investment in an orbital slot to be protected by changing the communication functionability of an initial core spacecraft which is assigned to the orbital slot.
There also is a need for techniques which permit a spacecraft""s communication processing to be altered functionally, possibly multiple times, during its operational lifetime and which allows for direct intersatellite communications in the future. The present invention enables the communication functionality to be altered and to allow intersatellite communications to be added with a degree of economy and ease which is not available by using any of the known prior techniques.
One object of the present invention is to provide components which can be placed on a core or initial satellite and which enable and facilitate long distance intersatellite communication after the core satellite is placed into an orbital slot.
Another object of the invention is to provide components suitable for launching on a core satellite which perform ground to satellite communications immediately upon deployment, but which facilitate communication with additional components launchable with a less expensive supplemental satellite that enable direct long distance inter-satellite communication in the future.
Yet another object of the present invention is to provide components suitable for launching with a core satellite to allow communication with a supplemental satellite on which new long distance intersatellite communication can be carried out, but which does not require duplication of the uplinks and downlinks built into the core satellite.
By using a component arrangement of the foregoing type, communication signals received by the core satellite may be routed to a supplemental satellite over an intersatellite short range link where they can be used to communicate with another satellite via a long range intersatellite link. Communication signals received from another satellite over the long range link may be sent back to the core satellite over the short range intersatellite link and inserted into a downlink signal chain for downlink transmission.
In one embodiment of the invention, there is an uplink receiver which is deployable with a first satellite and which is capable of receiving communication signals from a first ground based communication station. A first processor, such as a bent pipe repeater, is deployable on the first satellite and is capable of processing signals from the uplink receiver. A two-way intersatellite communications link terminal, deployable with the first satellite and operable within a first range, is capable of communication with a second two-way communication link terminal deployable with the second satellite which is capable of receiving intersatellite signals from beyond the first range. A first switch, deployable with the first satellite, enables signals from the uplink receiver to be utilized by the first intersatellite communication link terminal or the first processor. A downlink transmitter, deployable with the first satellite, is capable of transmitting signals to a second ground based communication station. A second switch, deployable with the first satellite, enables signals from the first intersatellite link terminal or the first processor to be utilized by the downlink transmitter.
By employing apparatus of the foregoing type, the communication capabilities of the first satellite can be enhanced by launching the second satellite, preferably into the orbital slot of the first satellite. Long range intersatellite communications can be performed on the second satellite and communicated to the ground through the uplink and downlink transmitters on the first satellite. By using apparatus and methods of the foregoing type, the processing functionality of the satellite communication system can be altered and modified with a degree of ease and economy and not available by the use of the known prior techniques.
The foregoing techniques enable the satellite system operator to defer major decisions about the need to incorporate long range intersatellite links until the need materializes and/or the required technology/protocols have time to mature. A spacecraft can be launched and activated. Then, through the addition of a supplemental satellite, its role in the communications network that it serves can be altered/expanded to meet changing market conditions or operational requirements. In this way, orbital slots can be populated with satellites whose productive lifetime is protected from obsolescence.